A variety of track suspension systems have been employed in the prior art. A commonly encountered track suspension system includes a front idler wheel and a rear drive sprocket over which the continuous track is draped. Another suspension system is known as a triangular track system in which a track frame is pivotally mounted to a pivot shaft on a vehicle. Front and rear idler wheels are mounted at opposing ends of the track frame. The drive sprocket is rotatably mounted on the vehicle above the pivot shaft. A continuous track engages the drive sprocket and the two idler wheels in a triangular configuration. The advantage of the triangular configuration is that the drive sprocket is mounted above the ground surface, thus freeing it from drit and debris, prolonging its life. Additionally, the drive sprocket construction can be lightened because it is not required to carry a part of the vehicle load.
A distinction of the triangular track system is that as the track frame rocks about the pivot shaft, the geometry associated with the idler wheels and the drive sprocket changes. For example, as the track frame rocks from the horizontal, the circumference around the idler wheels and drive sprocket is reduced, thus causing slack in the track. Slack in the track is undesirable because it allows the track to become disengaged from either the idler wheels or sprocket or both. In addition, a certain amount of preload tension in the track is desirable to maintain the track, idler wheels and sprocket in engagement. The preload tension should be minimal in value and remain essentially constant to minimize wear on the component parts of the track system.
On existing triangular track systems, the angle through which the track frame swings is quite small (on the order of .+-.3.degree.). The resulting change in circumference is quite small and is usually ignored. In a rough terrain application, such as a log skidder, however, the angle through which the track frame is required to rotate is quite large (on the order of .+-.30.degree.). The change in circumference brought about by the relatively large rotational angle is significant. A way to minimize the circumference change must therefore be found.